1. Field of the Invention
The present invention relates to a spill control apparatus for a fuel injection system, in which a sleeve is externally fitted to a rotor and the position of the sleeve relative to the rotor is used to adjust the communication timing with which a port at the rotor and a port at the sleeve come into communication with each other. More specifically, the present invention is adopted in distributor type fuel injection systems in which a rotor that rotates in synchronization with an engine is fitted with plungers that are radially slidable, and the plungers are caused to make reciprocal movement by a cam ring, to vary the volumetric capacity of the compression space formed at the rotor.
2. Description of the Related Art
In the known art, inner-cam type fuel injection systems characterized in that ports are formed at a rotor and a sleeve externally fitted to the rotor include, for instance, the one disclosed in Japanese Unexamined Patent Publication No. S60-79152 and the one disclosed in Japanese Unexamined Patent Publication No. H8-270521.
In the former system, a concentric inner-cam (cam ring) is provided around a rotating fuel distribution member (rotor) and force-feed plungers are provided at the cam surfaces formed on the inside of this inner-cam via rolling elements or the like, to cause the force-feed plungers to move reciprocally in a radial direction relative to the rotating fuel distribution member. The rotating fuel distribution member is provided with, a pump chamber (compression space) whose volumetric capacity is varied by the force-feed plungers, an intake port to take fuel into the pump chamber during the intake process, a distribution port for delivering the fuel pressurized in the pump chamber during the force-feed phase and spill ports for cutting off fuel delivery The spill ports are formed with a ring-like member (control sleeve) which covers the cutoff port externally fitted on the rotating fuel distribution member.
A reed-like groove is provided on the internal circumferential surface of the ring-like member or the external circumferential surface of the rotating fuel distribution member. By forming a spill start edge which is inclined relative to the generating line at the reed-like groove and causing the ring-like member to move in the axial direction of rotating member, the spill start timing (cutoff timing) is varied, to allow the injection amount to be varied.
The latter, which is an inner-cam type fuel injection system, has a structure basically identical to that of the former system, with a control sleeve externally fitted to the distribution member and timing with which inflow/outflow ports (rotor ports) formed in the distribution member and intake/cutoff ports (sleeve ports) formed in the control sleeve come into communication can be varied by relatively displacing the control sleeve in the axial direction. In this fuel injection system, each of the communication start edges at the inflow/outflow ports and the intake/cutoff ports is constituted by the oblique side that is inclined in the axial direction. In particular, the length of the intake/cutoff ports (sleeve ports) in the axial direction is shorter than the length of the inflow/outflow ports (rotor ports) in the axial direction.
Forming a spill start edge on an incline as in the former example is known in the prior art, and because this spill start edge determines the amount of fuel to be injected, it must be machined to a high degree of precision. However, the formation of an edge with satisfactory precision cannot be guaranteed by merely creating an indented groove on the internal circumferential surface of the ring-like member or the external circumferential surface of the rotating fuel distribution member to form a spill start edge as described above. Therefore, the inventor of the present invention has been studying structures that are formed by superimposing a reed-like indented portion 52 (second indented portion) for cutoff, upon the pond-like indented portion 51 (first indented portion).
Such a reed-like indented portion 52 is formed by cutting a groove of a specific width that is inclined relative to the shaft center as shown in FIG. 6B, using a circular cutter or the like. However, when this is formed arbitrarily, i.e. without consideration for its relation with the existing pond-like indented portion 51, scars 55 may result on the sliding contact surfaces of the rotating member 53 and the sleeve 54, or the rotating member 53 and the sleeve 54 may become seized.
Based on their research and investigations, the inventors of the present invention have discovered that if an end portion 52a of the reed-like indented portion 52, which is to the rear in the direction of rotation, protrudes from the pond-like indented portion 51 and a corner 56 which progressively narrows toward the rear relative to the direction of rotation is formed at this reed-like indented portion 52, fine dust particles 57 are likely to collect at this corner 56. In addition, because the reed-like indented portion 51 is oriented upward in the shape of an arc with its cutting start and cutting finish end cut are cut by a circular cutter (see FIG. 6B), the dust particles 57 which have collected in the corner portion are guided to the space between the rotating member 53 and the sleeve 54, increasing the likelihood of the sliding surfaces becoming scarred or seized.
As long as the reed-like indented portion is shaped in such a manner that the dust particles have a tendency to move toward the sliding contact surface, in order to avoid seizure, the clearance between the rotating member 53 and the sleeve 54 cannot be reduced, which, in turn, makes it difficult to increase the fuel injection pressure and stabilize fuel injection at low speed.
Also, in the latter example, because the inflow/outflow ports 31 (rotor ports) formed on the distribution member 8 are longer in the axial direction than the intake/cutoff ports 35 (sleeve ports) formed at the control sleeve 34 as shown in FIG. 7, the range over which the intake/cutoff ports 35 communicates with the inflow/outflow ports 31 is limited to the range (.delta.) of the intake/cutoff ports 35, as shown in FIG. 8. The ranges (.epsilon.) over which the intake/cutoff port 35 is not present form pockets of space that are blocked by the internal circumferential surface of the control sleeve 34 (the area shown in diagonal lines), causing the compressed fuel to swirl in this blocked-off space. This in turn causes dust particles to collect in the blocked-off area and these dust particles is drawn into the gap between the distribution member 8 and the control sleeve 34, scarring their sliding contact surfaces and inducing seizure of the distribution member 8 and the control sleeve 34 in a manner similar to that described above.